The present invention relates to a display unit for constituting a large display screen of a display apparatus and, more particularly, to an improved display unit in which the distribution of luminance over the entire area of the display panel is uniform.
A conventional liquid crystal display unit, namely, a typical display unit for constituting a large display screen of a display apparatus, is illustrated in FIG. 10. In FIG. 10, there are shown a case 1, a guide groove 1a formed in the case 1, a liquid crystal panel 2, namely, a display panel, a straight fluorescent lamp 3 disposed within and held on the case 1 and provide at the opposite ends 3a thereof with bases 3b, a reflecting plate 4 holding the liquid crystal panel 2 and disposed within and held on the case 1 so as to reflect the light emitted by the fluorescent lamp 3 toward the backside of the liquid crystal panel 2, a diffusion film 5 held on the reflecting plate 4 to diffuse the light emitted by the fluorescent lamp 3 so that the backside of the liquid crystal panel 2 is irradiated, a D/A conversion circuit board 6 having a circuit capable of D/A conversion, a liquid crystal driving circuit board 7 mounted with a LSI for driving the liquid crystal panel 2 on the basis of analog signals provided by the D/A conversion circuit board 6, and a connector 8 for connecting the fluorecent lamp 3 to a power source, not shown.
A plurality of the liquid crystal display units thus consituted are mounted on a supporting frame by receiving the guide rails of the supporting frame in the guide grooves 1a of the liquid crystal display units, respectively, so as to form a display screen of a predetermined size and shape.
In operation, digital signals corresponding to a still picture or an animated picture, produced by an external controller, not shown, are converted into corresponding analog signals meeting the characteristics of the liquid crystal by the circuit of the D/A conversion circuit board 6. The analog signals thus produced are transmitted through the liquid crystal driving circuit board 7 to the liquid crystal panel 2. Since the liquid crystal panel 2 itself is a nonluminous element, a light source is necessary for illuminating the liquid crystal panel 2. The fluorescent lamp 3 is lighted by a fluorescent lamp starting device, not shown to illuminate the liquid crystal panel 2. The light transmissivity of the liquid crystal panel 2 is controlled according to the analog signals given thereto so that an image corresponding to the still picture or the animated picture is displayed on the liquid crystal panel 2.
In such a conventional display unit, since the fluorescent lamp 3 is provided, at the opposite ends thereof with bases and filaments, respectively, the luminance of the end section is lower than that of the middle section of the fluorescent lamp. Furthermore, the luminance of the end section of the fluorescent lamp decreases with the passage of time more remarkably than the luminance of the middle section of the same and the black stain of the end section increases with time, which is a specific phenomenon to the fluorescent lamp. When a large display screen is formed by arranging a plurality of the liquid crystal display units having such characteristics on a supporting frame, not shown, the irregularity of the luminance of the liquid crystal display panels forming the display screen becomes conspicuous, thus reducing the quality of the displayed image.